The present invention relates to multilayer plastic preforms and containers with co-extruded liners having an oxygen scavenger layer, and a method for making such articles.
Many foods and beverages need protection from oxygen to maintain their quality and taste. Producers of such products seek packages that provide sufficient protection for longer-lasting taste and improved shelf life. Some common examples of oxygen-sensitive products include beer, citrus juices, and tomato-based products.
Oxygen can come into contact with the product content of plastic or polymer containers from one or more of several sources. First, oxygen can reside in the internal volume of the container, either as part of the filled product or as part of the xe2x80x9cheadspacexe2x80x9d remaining above the product after firing. Second, oxygen from outside the container can permeate through the walls of the container or enter at the closure. Lastly, because oxygen resides naturally in plastic, once the container is filled it will release some of the resident oxygen and it will migrate to the inside of the container. Tests have shown that the latter source can have a very significant effect on the shelf-life of a product.
In the art of making plastic containers, various techniques have been employed to inhibit or prevent the ingress of exterior oxygen into the container and to scavenge the oxygen present inside the walls of the packaging. Several methods currently used to better regulate the exposure of the contents to oxygen incorporate different synthetic plastic resins having gas-absorbing capabilities into the structure of the packaging. The intention is that the layers of scavenging material will intercept and/or scavenge gases, such as oxygen, as their molecular compositions pass through the walls of the container and thereby protect the product therein.
In an effort to protect the oxygen-scavenging layer for the aforementioned use, some manufacturers of multilayered packages surround the oxygen-scavenging layer with one or more layers of known high-barrier materials. The high-barrier materials serve to reduce the oxygen transmission rate and to protect the oxygen-scavenging layer from premature activation.
However, in the production of bottles and containers that are used to package oxygen sensitive products, several practical issues are encountered. For instance, where foods, beverages, and other consumable items are involved, federal regulations often require that the innermost polymer layer that is in contact with the product contents must be approved for such use. In a number of cases, applicable regulations establish a minimum wall thickness for the innermost contact layer that must be maintained.
A notable disadvantage is encountered when conventional co-injection molding processes are used to form a preform that includes an oxygen-scavenging layer as part of an encapsulated core layer. In order for such a process to provide a preform with an innermost layer of FDA-approved material (e.g. virgin PET), the outermost layer of the co-injected structure will inherently consist of an equal thickness of the same material. In instances where a less expensive thermoplastic material (e.g. post consumer recycled PET) is available, placing such a corresponding thickness of the more expensive material on the outermost surface of the structure of a liner or preform, where it does not affect the contents, adds unnecessary expense.
Processes that produce a multilayer preform by injecting one layer of a thermoplastic material over the next can eliminate the aforementioned disadvantage of having the same thermoplastic material positioned on the innermost and outermost layers of the preform. However, such processes involve the use of multiple sets of costly rigid molds. Furthermore, because the molds are solid physical items, dimensionally variation of the wall thickness of the articles cannot be readily programmed or modified as it can be by an extrusion process.
In light of the limitations of the prior art, some objects of the present invention are to provide improved multilayered oxygen-scavenging plastic preforms and resultant containers wherein:
(a) the structure includes a liner with a flexible layering scheme in which the innermost layer of the liner and outermost layer(s) of the liner and preform can be comprised of different materials;
(b) the wall thickness of individual layers of the various articles may be uniform or controllably varied along their lengths;
(c) oxygen scavengers and barrier materials are more effectively utilized;
(d) the quality and shelf-life of oxygen sensitive products is improved; and
(e) the preforms and containers can be commercially produced in an efficient and cost effective manner with minimal additional capital investment.
In carrying out the above objects, a preform for forming a hollow blow molded plastic container is provided with a closed base, a multilayer body-forming portion extending from the base, and an open neck portion that extends from the body portion. The body portion includes a co-extruded inner liner that includes (a) an innermost polymer layer, (b) at least one oxygen-scavenging layer, and (c) at least one high-oxygen barrier layer for retarding the migration of gases and moisture therethrough. An outermost layer is molded over the inner liner to form a preform. The liner and preform are formed so that the wall thickness of the individual layers can easily be varied along their lengths, however, at any given point along the length of the co-extruded liner (a) the wall thickness of the innermost polymer layer is less than 0.50 of the wall thickness of the inner liner and (b) the wall thickness of the inner liner is less than 0.25 of the total wall thickness of the preform body portion. Moreover, by the nature of the process, the innermost layer and the outer molded layer of the liner and the preform can be comprised of different polymer materials.